The major objective of this proposal is to define quantitatively and temporally the input-output relations involved in the reflex vascular changes in response to hemorrhage. Specific attention is directed toward the isolation of the activities of cardiac receptors and of arterial baroreceptors using analogs of hemorrhage and computer controlled pumping of blood. Attention is further directed toward defining the relationship of reflex changes in blood flow and blood volume in specific vascular beds to the activity of cardiovascular receptors. Relationships are described by cross-correlating the varaibles of interest and by testing linear models. Finally, experiments are designed to begin to identify the central neural pathways directly involved in the reflex vascular responses by using general and specific lesions and electrical stimulation. Experiments are also designed using single neuron recording to begin to identify the central neural encoding of the activity of the different cardiovascular receptors.